Method and apparatus for generating HF signals for determining a distance and/or a speed of an object

ABSTRACT

The present invention provides a method for generating HF signals for determining a distance and/or a speed of an object, having the following steps: generating a pulsed demodulated signal ( 6 ′) from a first signal ( 3 ) and a second signal ( 4 ) in a signal generator ( 31; 1, 2 , M 1, 7, 8 ); with a transmitting device ( 20 ), sending the pulsed modulated signal ( 6 ′) in the direction of an object ( 40 ); with a receiving device ( 21 ), receiving a pulsed signal ( 6 ″) reflected by the object ( 40 ); generating a pulsed demodulated signal ( 4 ″) from the received signal ( 6 ″) and the first signal ( 3 ) in a first signal processor ( 32 ; M 2, 15 ); and generating a coherent signal ( 23 ) from the pulsed demodulated signal ( 4 ″) and the second signal ( 4 ) and a noncoherent signal ( 22 ) from the pulsed demodulated signal ( 4 ″) in a second signal processor ( 33 ; M 3, 16, 17, 18 ). The present invention also provides an apparatus for generating HF signals for determining a distance and/or a speed of an object.

PRIOR ART

The present invention relates to a method and an apparatus forgenerating HF signals for determining a distance and/or a speed of anobject.

Systems for measuring the distance and speed of static objects orobjects in motion using high frequency (radar) are becoming more andmore important, especially in the automotive industry. Detecting objectsby radar is already used today for parking aids and speed governingsystems with distance measurement for great distances, such as thefollowing distances on limited-access highways. Additional areas wheresuch systems can be used are monitoring the so-called blind spot of avehicle, pre-crash detection for the sake of controlled actuation ofairbags and belt tighteners, so-called backing aids, and also speedgoverning systems, which because of the higher resolution of the systemmake operation possible even at lesser distances, as in travel betweencities or in city traffic.

One known system is the radar front end system known as SRR (for shortrange radar), which operates at a frequency of 24.125 GHz and makes itpossible to determine distance by transmitting HF pulses with a typicalwidth of 400 ps and determining their transit time.

Given the restrictions to permission for radiation emissions in theUnited States and in future in Europe as well, there is a need to reducethe transmission power of such systems, but doing so limits the range ofsuch a system. A predetermined range must absolutely be maintained,however, to assure safe operation, for instance in this kind ofdistance-measuring radar for a speed governing system.

ADVANTAGES OF THE INVENTION

The method and apparatus according to the invention for generating HFsignals for determining a distance and/or a speed of an object, havingthe characteristics of claims 1 and 18, respectively, have the advantageover the known embodiments that a better noise factor and hence anincreased detection distance can be achieved, so as to compensate for apossible necessary reduction in power; that is, even if the transmissionpower is reduced, all the necessary functions can be performed,especially while keeping system and sensor costs unchanged.

The concept on which the present invention is based is to apply asuperheterodyne concept, taking necessary modifications into account, tothe architecture of the known SRR (short range radar).

In the present invention, the problem addressed at the outset is solvedin particular by providing that a pulsed modulated signal is generatedin a signal generator from a first signal and a second signal and isbroadcast via a transmitting device, while via a receiving device apulsed signal reflected by an object is received, and from that a pulseddemodulated signal is generated with the aid of the first signal in afirst signal processor, and a coherent signal is generated from thispulsed demodulated signal with the aid of the second signal, and anoncoherent signal is generated from the pulsed demodulated signal in asecond signal processor.

Advantageous refinements and improvements of the method defined by claim1 and the apparatus defined by claim 18 are recited in the dependentclaims.

In a preferred refinement, in the signal generator, the first signal isgenerated with a first HF oscillator and the second signal is generatedwith a second HF oscillator, and these signals are modulated in amodulator into a modulated signal pair. This has the advantage that themodulation of the second signal (coherence oscillator signal or coho) tothe first signal (HF oscillator stalo) can be done in narrow-bandfashion by the modulator upstream of an HF switch device. Anotheradvantage is that the modulator can in principle be embodied inunbalanced form and consequently can be based on a single diode.

In a further preferred refinement, the modulated signal pair isconverted in a filter device, in particular a high-pass filter, into afiltered modulated signal and, by a first switch device, into a pulsedmodulated signal. This has the advantage that the unwanted lowersideband created by the modulation can be suppressed by filtering, forinstance using an etched stripline filter on the HF substrate or usingan integrated filter for the sake of saving space. If the firstmodulator comprises one diode (unbalanced up-converter), then in theresultant mixed product a considerable residual carrier remains at 24GHz. This carrier must also be suppressed by the high-pass filter. If abalanced mixer is used, then the residual carrier, as a mixed product,is largely avoided.

In a further preferred refinement, the first signal processor convertsthe received signal into a demodulated signal with the aid of the firstsignal in a second modulator and into a pulsed demodulated signal bymeans of a second switch device. This makes it possible to utilize theamplitude information of the transmission signal, not by means of aswitch device in the HF branch as in SRR, but instead by means of aswitch device after the first demodulation. The switch at the lowfrequency is more economical to make. The sampling of the low-frequencysignal is done at a higher signal level, for instance afterlow-frequency preamplification.

In a further preferred refinement, the pulsed demodulated signal isconverted into the noncoherent envelope curve signal by means of arectifier and a filter device, in particular a low-pass filter. This hasthe advantage that by this envelope curve detection, in which the phaseinformation is lost because of the noncoherent demodulation by therectifier, in contrast to SRR no zero crossovers are generated, and itis therefore possible to dispense with complicated I/Q demodulation inthe second modulator.

In a further preferred refinement, the pulsed demodulated signal isdemodulated in a third modulator with the aid of the second signal toform a twice-demodulated pulsed signal. The advantage of this step isthat thus the pulsed demodulated signal, which contains the distanceinformation, is subsequently demodulated with the second signal in thethird modulator, and after evaluation, the speed determination can bedone using the Doppler effect. Because of the coherent demodulation, thephase information is preserved.

In a further preferred refinement, the pulsed, twice-modulated signal isdelivered to an integrator, which integrates the signal to form thecoherent signal. This makes it possible to evaluate the coherent signaland consequently to measure the speed by way of the Doppler effect.

In a further preferred refinement, pulse signals for activating theswitch devices are generated in a pulse generator. As a result, precisetriggering of the first and second switch devices is made possible.

In a further preferred refinement, a clock signal that is alternatinglyshifted slightly externally and internally by a fixed mean value of apredetermined period length is combined in a multiplexer of the pulsegenerator, and via pulse shapers, activation signals of the switchdevices are generated. As a result, an advantageous non-equidistantpulse pattern of the transmitted HF signal is made possible.

In a further preferred refinement, the frequency of the first signal isapproximately 21.5 GHz, and the frequency of the second signal isapproximately 2.5 GHz. This has the advantage that the resultanttransmission frequency (in this case, 24 GHz) is in the ISM band around24.125 GHz, which is necessary since residual broadcasting of thiscarrier is unavoidable and must occur in an approved band.

In a further preferred refinement, the frequency of the first signal isapproximately 24 GHz, and the frequency of the second signal isapproximately 3.5 GHz. This has the advantage that the resultanttransmission frequency of 25 GHz to 27.5 GHz is designed for a desiredtransmission outside prohibited bands, to avoid permit problems.

In a further preferred refinement, the signal received from thereceiving device is amplified in a low-noise amplifier before it isdelivered to the first signal processor. This makes a further reductionof the noise factor of the entire radar system by a further 6 dBpossible.

In a further preferred refinement, the demodulated signal is amplifieddownstream of the second modulator in an amplifier, in particular alow-frequency preamplifier, before it is delivered to the second switchdevice. As a result, the signal level is advantageously raised.

DRAWINGS

Exemplary embodiments of the invention are shown in the drawings anddescribed in further detail in the ensuing description.

Shown are:

FIG. 1, a schematic illustration of an apparatus, for explaining themode of operation of a first embodiment of the present invention;

FIG. 2, a block diagram, for schematically illustrating an apparatus ina second embodiment of the present invention; and

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In the drawings, the same reference numerals stand for the same orfunctionally identical components.

FIG. 1 is a schematic illustration of an apparatus for explaining themode of operation of a first embodiment of the present invention.

In FIG. 1, a pulse-based superheterodyne radar system, particularly forshort range, is shown. In a first signal source 1, a firsthigh-frequency signal 3 (stalo) of the frequency f_(ST) is generated. Ina second signal source 2, a second high-frequency signal 4 (coho) of thefrequency f_(LF) is generated. In a first modulator M1, which is basedfor instance essentially on a single diode and is embodied in unbalancedform, the second signal 4 is modulated to the first signal 3. Themodulation essentially corresponds to multiplication in the time range,or in other words addition in the frequency range, resulting in amodulated signal pair 5 that has the frequencies f_(ST)±f_(LF).

The unwanted lower sideband f_(ST)−f_(LF) of the modulated signal pair 5and also the residual carrier f_(ST) are suppressed in a filter device7, for instance an etched stripline filter on the HF substrate or anintegrated filter (to save space), so that a filtered modulated signal 6of the frequency f_(ST)+f_(LF) is carried onward to a first switchdevice 8.

A PRF (pulse repeated frequency) signal 9, permanently slightly shiftedexternally with respect to a predetermined mean value of a periodlength, is combined with a PRF (pulse repeated frequency) signal 10,internally slightly shifted, in a multiplexer 11. The result is aconstantly slightly varied repetition rate, for instance in the rangebetween 350 and 450 ns, so as to avoid equidistant activation signals34, 35 that are generated by a pulse shaper 12 on the receiver side anda pulse shaper 13 on the transmitter side.

The external PRF signal 9 preferably originates in a cross echo partner(not shown). The detection range for cross echo measurement is locatedsymmetrically relative to the semiaxis at the distance between thetransmitter and the receiver. The PRF signal 9 is delivered to thereceiver via an internal delay 12. A possible carrier frequency offsetof the transmitter and receiver, caused for instance by tolerances oraging, is slight in comparison to the bandwidth of the low-frequencychannel. It is therefore possible for even a frequency-offset signal inthe noncoherent reception path to be undergo envelope curvedemodulation.

In indirect triangulation or in the cross echo method, a first sensortransmits a signal at a first carrier frequency, and at least onesecond, laterally spaced-apart sensor, for instance at a distance of 1m, receives the first signal reflected by an object. The second sensorcan be designed for a slightly different carrier frequency, as long asthe frequency difference does not exceed the bandwidth of thelow-frequency channel. A centric directional characteristic is madepossible by the at least two sensors laterally spaced apart from oneanother.

The pulse shapers 12, 13 define the pulse duration, such as 400 ps or 1ns, at which the first switch device 8, or a second switch device 15, isactivated. The ON time of the first switch device 8 is controlled bymeans of the activation signal 35, so that from the filtered modulatedsignal 6, a pulsed modulated signal 6′ is created, which is broadcastvia a transmitting device 20, such as an antenna.

The pulsed modulated signal 6′ broadcast via the antenna 20 is reflectedat an object 40 and received by a receiving device 21. A signal 6″received by the receiving device 21 passes through a low-noise amplifier14 and is delivered to a second modulator M2. The second modulator M2demodulates the received signal 6″ using the first signal 3, and themixer M2 outputs a demodulated signal of the frequency f_(LF).

This demodulated signal 4′ is delivered to a second switch device 15,which as a function of the activation signal 34 generates a pulseddemodulated signal 4″ at the frequency f_(LF). The demodulated signal 4′can be delivered, upstream of the second switch device 15, to anamplifier device (14′), such as a low frequency preamplifier, in orderto raise the signal level. In a third modulator M3, the pulseddemodulated signal 4″ is demodulated with the second signal 4 of thesecond HF oscillator (coho), that is, the coherence oscillator, so thata twice-demodulated pulsed signal 4′″, that is, a basic pulse trainwhere f=0, is created.

Since the pulsed demodulated signal 4″ contains the desired distanceinformation for the distance between the apparatus and the object 40,the signal 4′″ demodulated with the coherent signal 4, after evaluationof the signal 4′″ in an integrator 16, makes it possible to determinethe speed on the basis of the Doppler effect, using the coherent signal23. Parallel to this, by means of a rectifier 17, the pulsed demodulatedsignal 4″ is subjected to a noncoherent demodulation, with a loss of thephase information. This envelope curve detection, however, does notgenerate any zero crossovers, since there is no phase dependency, andtherefore it is possible to dispense with a complicated I/Q modulation(in-phase quadrature demodulation) in the mixer M2. The rectifier 17 isfollowed by a filter device 18, such as a low-pass filter, at the outputof which a noncoherent signal 22, for instance for determining thedistance, is output by the cross echo method and static targets.

The choice of the frequency f_(LF) of the second signal, such as 2.5GHz, is determined on the one hand from the requirements for a feasibleHF filter, which are not as hard to meet at a higher frequency f_(LF),and the requirements for the noncoherent envelope curve demodulation ofthe pulsed demodulated signal 4″. The cut-off frequency of thedownstream low-pass filter advantageously makes a precise distinctionbetween the boundaries of the baseband (rectified signal around 0 Hz)and the frequency f_(LF) at 2.5 Ghz. The result is a useful limitfrequency, in this example, of 1.25 GHz.

In principle, the bandwidth of the frequency f_(LF) must encompass thedouble-sided HF pulse spectrum. At an HF pulse width of 500 ps, the 10dB bandwidth is at 2.4 GHz, and the 20 dB bandwidth is at 3.4 GHz,assuming a gaussian pulse shape in the time range. In the branch for theenvelope curve detection, the possible Doppler shifts of up to 10 kHzcan be ignored. For reasons of cost, the mixer M3 can be embodied as asingly balanced mixer, since in determining the distance no zero pointsoccur, and for the speed determination, an I/Q signal originating in analternative I/Q mixer is not absolutely necessary.

The mixer M2 is designed to be singly balanced, so as to profit from thesuppression of the amplitude noise of the first HF source (stalo). Thelow-noise amplifier can optionally be dispensed with, since because ofthe improvement in the noise factor of the entire radar system, thefurther 6 dB of this amplifier are not absolutely necessary to achievethe planned functions, and hence this cost-intensive component mayoptionally be omitted. The third mixer M3 can be designed in thisfrequency range as an economical integrated Gilbert cell mixer and canfurnish the requisite amplification without further amplifier stages, orwith a preamplifier 14′, between the mixer M2 and the second switchdevice.

FIG. 2 is a block diagram for explaining a second embodiment of thepresent invention.

In FIG. 2, a pulse generator 30 is shown, which furnishes an activationsignal 35 for a switch device in a signal generator 31 and an activationsignal 34 for a switch device in a first signal evaluation device 32. Apulsed modulated signal 6′ of the frequency f_(ST)+f_(LF) is generatedin the signal generator 31 and is delivered to a transmitting device 20,such as an antenna. In addition, the signal generator 31 outputs asignal (coho) at the frequency f_(LF) to a second signal processor orsignal output device 33, as well as a further signal (stalo) at thefrequency f_(ST) to the first signal processor 32.

The pulsed demodulated signal 6′, broadcast via the transmitting device20, strikes an object 40 and is reflected by it. The reflected signal 6″received by a receiving device 21 is delivered to the first signalprocessor 32. In this signal processor 32, from the received signal 6′together with the signal 3 (stalo) and the activation signal (34), apulsed demodulated signal 4″ at the frequency f_(LF) is formed, which isdelivered to the second signal processor 33.

From this pulsed demodulated signal 4″ and the signal 4 (coho), anoncoherent signal 22 for a cross echo method and for measuring thedistance from static targets is generated in the signal processor orsignal output device 33. The signal processor or signal output device 33also generates a coherent signal, from which the speed of the object 40relative to the transmitting device 20 or receiving device 21 can beevaluated. Here, the words coherent and noncoherent refer to the signal4 (coho), which can also be called a coherence signal, with coherencemeaning the fixed phase relationship between two signals.

In the present invention, preferably two frequency pairs for the firstsignal of the frequency f_(ST) and the second signal of the frequencyf_(LF) are provided. These are first a first frequency of 21.5 GHz forf_(ST) (stalo) and a second frequency of 2.5 GHz for f_(LF) (coho), andsecond, a first frequency of 24 GHz for f_(ST) (stalo) and a secondfrequency of 2.5 GHz to 3.5 GHz f_(LF) (coho).

The prerequisite for achieving this system is that the residual carriermust be less than −30 dBm, which can be achieved by means of a switchinsulation of 50 dB.

Although the present invention has been described above in terms ofpreferred exemplary embodiments, it is not limited to them but insteadcan be modified in manifold ways.

For example, concrete component specifications especially, such as adiode for a mixer or a stripline grid filter for the filter device, canalso be simulated using other components or devices.

1. A method for generating HF signals for determining a distance and/ora speed of an object, having the following steps: generating a pulsedmodulated signal (6′) from a first signal (3) and a second signal (4) ina signal generator (31; 1, 2, M1, 7, 8); with a transmitting device(20), sending the pulsed modulated signal (6′) in the direction of anobject (40); with a receiving device (21), receiving a pulsed signal(6″) reflected by the object (40); generating a pulsed demodulatedsignal (4″) from the received signal (6″) and the first signal (3) in afirst signal processor (32; M2, 15); and generating a coherent signal(23) from the pulsed demodulated signal (4″) and the second signal (4)and a noncoherent signal (22) from the pulsed demodulated signal (4″) ina second signal processor (33; M3, 16, 17, 18).
 2. The method of claim1, characterized in that from the coherent signal (23), an approachspeed of the object (40) is determined.
 3. The method of claim 1,characterized in that from the noncoherent signal (22), a distance fromthe object (40) is determined.
 4. The method of claim 1, characterizedin that in the signal generator (31; 1, 2, M1, 8), the first signal (3)is generated with a first oscillator (1) and the second signal (4) isgenerated with a second oscillator (2), and these signals are modulatedinto a modulated signal pair (5) in a first modulator (M1).
 5. Themethod of claim 4, characterized in that the modulated signal pair (5)is converted, in a filter device (7), in particular a high-pass filter,into a filtered modulated signal (6) and, by a first switch device (8),into a pulsed modulated signal (6′).
 6. The method of claim 1,characterized in that the first signal processor (32; M2, 15) convertsthe received signal (6″) with the first signal (3) into a demodulatedsignal (4′) in a second modulator (M2) and into a pulsed demodulatedsignal (4″) by means of a second switch device (15).
 7. The method ofclaim 1, characterized in that the pulsed demodulated signal (4″) isconverted into the noncoherent signal (22) by means of a rectifier (17)and a filter device (18), in particular a low-pass filter.
 8. The methodof claim 1, characterized in that the pulsed demodulated signal (4″) isdemodulated in a third modulator (M3) with the second signal (4) to forma twice-demodulated pulsed signal (4′″).
 9. The method of claim 8,characterized in that the pulsed, twice-modulated signal (4′″) isdelivered to an integrator (16), which integrates the signal to form thecoherent signal (23).
 10. The method of claim 1, characterized in thatpulse signals (34, 35) for activating the switch devices (8, 15) aregenerated in a pulse generator (30; 10, 11, 12, 13).
 11. The method ofclaim 10, characterized in that a clock signal (9, 10) that is slightlyshifted externally and internally in alternation by a fixed mean valueof a predetermined period length is combined in a multiplexer (11) ofthe pulse generator (30), and via pulse shapers (12, 13), activationsignals (34, 35) of the switch devices (15, 8) are generated.
 12. Themethod of claim 11, characterized in that in the pulse shapers (12, 13),pulses approximately 1 ns in length are formed.
 13. The method of claim10, characterized in that the clock signal (9, 10) that is slightlyshifted externally and internally in alternation by a fixed mean valueof a predetermined period length activates the switch devices (8, 15)every 350 ns to 450 ns.
 14. The method of claim 1, characterized in thatthe frequency of the first signal (3) is approximately 21.5 GHz, and thefrequency of the second signal (4) is approximately 2.5 GHz.
 15. Themethod of claim 1, characterized in that the frequency of the firstsignal (3) is approximately 24 GHz, and the frequency of the secondsignal (4) is approximately 3.5 GHz.
 16. The method of claim 1,characterized in that the signal (6″) received from the receiving device(21) is amplified in a low-noise amplifier (14) before it is deliveredto the first signal processor (32; M2, 15).
 17. The method of claim 1,characterized in that the determination of the distance of an object(40) is made in a cross echo method or by indirect triangulation with across echo partner.
 18. An apparatus for generating HF signals fordetermining a distance and/or a speed of an object, having: a signalgenerator (31; 1, 2, M1, 7, 8), for generating a pulsed modulated signal(6′) from a first signal (3) and a second signal (4); a transmittingdevice (20), for transmitting the pulsed modulated signal (6′) in thedirection of an object (40); a receiving device (21), for receiving apulsed signal (6″) reflected by the object (40); a first signalprocessor (32; M2, 15), for generating a pulsed demodulated signal (4″)from the received signal (6″) and the first signal (3); and a secondsignal processor (33; M3, 16, 17, 18), for generating a coherent signal(23) from the pulsed demodulated signal (4″) and the second signal (4)and for generating a noncoherent signal (22) from the pulsed demodulatedsignal (4″).
 19. The apparatus of claim 18, characterized in that thesignal generator (31; 1, 2, M1, 7, 8) has a first oscillator (1) forgenerating the first signal (3), a second oscillator (2) for generatingthe second signal (4), and a first modulator (Ml) for modulating the twosignals (3, 4) to form a modulated signal pair (5).
 20. The apparatus ofclaim 19, characterized in that the signal generator (31; 1, 2, M1, 7,8) has a filter device (7), in particular a high-pass filter, forconverting the modulated signal pair (5) into a filtered modulatedsignal (6) and a first switch device (8), for converting the filteredmodulated signal (6) into a pulsed modulated signal (6′).
 21. Theapparatus of claim 18, characterized in that the first signal processor(32; M2, 15) has a second modulator (M2), for converting the receivedsignal (6″) with the first signal (3) into a demodulated signal (4′),and a second switch device (15), for converting the demodulated signal(4′) into a pulsed demodulated signal (4″).
 22. The apparatus of claim18, characterized in that the second signal processor (33; M3, 16, 17,18) has a rectifier (17) and a filter device (18), in particular alow-pass filter, for converting the pulsed demodulated signal (4″) intothe noncoherent signal (22).
 23. The apparatus of claim 18,characterized in that the second signal processor (33; M3, 16, 17, 18)has a third modulator (M3) for demodulating the pulsed demodulatedsignal (4″) with the second signal (4) into a twice-demodulated pulsedsignal (4′″).
 24. The apparatus of claim 23, characterized in that thesecond signal processor (33; M3, 16, 17, 18) has an integrator (16) forintegrating the pulsed, twice-demodulated signal (4′″) into the coherentsignal (23).
 25. The apparatus of claim 18, characterized in that theapparatus has a pulse generator (30; 10, 11, 12, 13), for generatingpulse signals (34, 35) for activating the switch devices (8, 15). 26.The apparatus of claim 25, characterized in that the pulse generator(30; 10, 11, 12, 13) has a multiplexer (11) and pulse shapers (12, 13)for generating a clock signal (9, 10) that is slightly shiftedexternally and internally in alternation by a fixed mean value of aperiod length, for activating the switch devices (15, 8).
 27. Theapparatus of claim 18, characterized in that the modulators (M1, M2, M3)are mixers, and the first modulator (M1), in particular having onediode, is unbalanced, and the second and third modulators (M2, M3) aresingly balanced.
 28. The apparatus of claim 18, characterized in thatthe third modulator (M3) has an integrated Gilbert cell mixer.
 29. Theapparatus of claim 18, characterized in that an amplifier (14′), inparticular a low-frequency preamplifier, for raising the signal level isprovided between the second modulator (M2) and the second switch device(15).